Rainbow and hologram images on fabrics

ABSTRACT

A process is provided for making a fibrous sheet that produces rainbow and/or hologram images. A sheet having an outer surface composed of fibrous elements has its outer surface embossed with a pattern of fine grooves that are substantially aligned from fibrous element to fibrous element. In contrast, prior fabrics for producing rainbow or hologram images were laminated to plastic or metal foils having pre-embossed patterns of grooves. Sheets and fabrics of the present invention are free from such impermeable foils and retain desirable attributes of breathability and other aesthetic qualities.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 08/777,821, filedDec. 31, 1996, now U.S. Pat. No. 5,882,770, issued Mar. 16, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to sheets embossed with diffractiongrating and/or hologram patterns. More particularly, the inventionconcerns a fibrous sheet or fabric whereon the diffraction gratingand/or hologram pattern is embossed directly on a surface of the fibroussheet or fabric without detrimentally affecting the flexibility andbreathability of the sheet or fabric.

2. Description of the Prior Art

Rainbow and hologram images have been produced by diffracting light frompatterns of very fine grooves on the surface of various plastic sheetsor films. Such patterns are mass-produced by embossing the plasticsurface under heat and pressure with a metal die (or "stamper") havingin its face the desired pattern in relief Known methods for producinghologram images on fabrics generally are rather complicated anddetrimentally affect certain properties of the fabrics. For example,U.S. Pat. No. 4,956,040 discloses a method in which a precut foil havinga hologram pattern embossed on its surface is laminated between a clearpolyester coating and an adhesive scrim backing to form a laminate whichis then adhered to a woven fabric. International Patent Application WO91/12365 discloses forming a laminate of an outer metal foil bearing aholographic image, a middle layer of plastic size and a lower layer offabric. These two disclosures are typical of the many methods involvingproduction of a hologram pattern on a plastic film or metal foil layerwhich is laminated to the surface of a fabric. Although such processescan provide strong holographic images, the portions of the fabric thatare covered with the film or foil lose the breathability, flexibilityand surface tactile aesthetics of the original fabric without the filmor foil. International Patent Application WO 89/01063 and JapanesePatent Publication SHO 63-309639 disclose embossing a hologram patternon a thin plastic film, slitting the film into long ribbons of 1 to 20mm width, forming the ribbons into yarns and then making a fabric of theribbons. However, fabrics made with such yarns are limited to localizedglitter color effects and cannot produce large scale rainbow or hologramimages. Further, the dimensions of the slit-ribbon yarns are usually toolarge for the ribbons to be used in apparel fabrics. For apparelfabrics, fiber diameter typically is in the range of 0.001 to 0.1 mm.

In other methods aimed at providing hologram images on fabrics, seriesof fine grooves are formed on individual filaments which are then formedinto fabrics. For example, Japanese Patent SHO 62-170510 disclosessimultaneously co-spinning two molten polymers into a filament and thendissolving one of the two polymer components to form fine grooves on thefilament surface parallel to the axis of the filament. U.S. Pat. No.4,842,405 discloses another method in which the fine grooves are cut inthe surfaces of filaments with laser beams. Because the distancesbetween adjacent filaments in the yarn and fabric are not controlled tobe at multiples of groove width and because these filaments typicallyare made into yarns by plying, interlacing, crimping and/or twisting,the groove patterns are disrupted and fabrics made from such filamentyarns do not provide full rainbow or hologram images but provide onlyglitter points or line segments of glitter randomly distributed on thefabric surface.

In summary, with regard to diffraction or hologram images on fabrics,the art discloses how to produce either (a) large rainbow and hologramimages on impermeable plastic films or metal foils which are laminatedor stitched to the surface of the fabric, but with accompanyingdetrimental effects on the breathability and tactile aesthetics of thefabric or (b) fine, microscopic glitter points on fabrics made fromfilaments having fine longitudinal grooves without affecting otherfabric characteristics. Accordingly, an aim of the present invention isto provide a fibrous sheet or fabric having large rainbow and/orhologram images without incorporating an impermeable plastic or metalfoil that would detrimentally affect the flexibility and breathabilityof the sheet or fabric.

SUMMARY OF THE INVENTION

The present invention provides a fibrous sheet having an outer surfacecomprising fibrous elements embossed with a multiplicity of finediffraction grooves that are substantially aligned from fibrous elementto fibrous element and form a pattern that produces rainbow and/orhologram images when the sheet is viewed at an angle to incident light.Preferably the fibrous elements are of thermoplastic synthetic organicpolymers, most preferably of polypropylene, polyethylene, polyester ornylon.

The invention also provides a process for making the fibrous sheet thatproduces rainbow or hologram images. The process comprises the steps of(a) preparing a sheet of fibrous elements, (b) softening at least thefibrous elements on a surface of the sheet sufficiently to permit thefibrous elements on the sheet surface to be embossable under pressurewith a pattern of fine diffraction grooves; (c) placing the sheet on asupporting surface; (d) bringing a hard embosser having a pattern offine diffraction grooves thereon into direct contact with the surface ofthe fibrous sheet; (e) imposing sufficient load on the embosser for asufficient time to impress the pattern of fine diffraction grooves intothe surface of the fibrous elements on the surface of the sheet; (f)separating the sheet from the embosser; and (g) collecting the separatedsheet.

Optionally, softening step (b) may be performed simultaneously withsheet/embosser contacting step (d) and/or pressure application step (e).Preferably, the fibrous sheet is made of thermoplastic fibrous elementsof synthetic organic polymer and the fibrous elements are softened byheat or a solvent for the polymer. The process does not detrimentallyaffect the breathability, flexibility and aesthetic attributes of thestarting fibrous sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood by reference to thedrawings wherein:

FIG. 1 is an exploded schematic view of a preferred assembly of itemsfor batch-embossing fibrous sheet 10, the items including a hardembosser 12 (also called a "stamper"), release sheets 13, 13', rubbersheets 14, 14', flat metal plates 15, 15', and platens 16, 16' of aplaten press (not shown);

FIG. 2 is a schematic representation of a continuous embossing processsimilar to that in commercial use for embossing films, but also, withappropriate controls, suitable for embossing, in accordance with thepresent invention, fibrous sheets made from thermoplastic polymers,especially those having relatively low melting-temperature (e.g.,polyolefins) wherein fibrous sheet 21 is forwarded from feed roll 22,under idler roll 23, through a nip formed by rubber-coverbed roll 24 andheated, hard embossing roll 25 to windup roll 26; and

FIG. 3 is a schematic representation of a continuous roll embossingprocess designed to provide higher heat transfer rates and to attainhigher embossing temperatures wherein fibrous sheet 31 is forwarded fromfeed roll 32 into thermally insulated chamber 39 and then successivelyinto contact with the surface of heated rolls 33, 33' and 33", andheated embossing roll 37 and then to windup roll 38, sheet 31 beingpressed against embossing 37 by rubber roll 35 through endlessrelease-sheet belt 36 which proceeds around idler rolls 34 and 34'.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The meanings of various terms used herein are as follows. "Fibroussheet" means a knit, woven, spunbonded, spunlaced, stitchbonded, orfelted fabric, or the like.

"Fibrous element" means any fiber, filament, thread, yarn, microfiber,fibril or the like of natural or synthetic polymer.

"Fine grooves" means parallel grooves or segments of parallel groovesthat are spaced apart uniformly by about 0.1 to 10 micrometers (microns)and are at least 0.01 micron deep. The presence of groups of suchgrooves on a solid surface produces light diffraction patterns. Groupsof straight, parallel fine grooves, also known as "diffractiongratings", produce rainbow colors, referred to hereinafter as "rainbowimages". Clusters of parallel fine groove segments having straight,curved or wavy configurations, originated by a hologram imaging process,reproduce the original images in the form of hologram images.

The present invention provides a fibrous sheet having patterns of finegrooves on a surface of the sheet. The patterns of grooves producerainbow or hologram images that are visible to the naked eye when thesheet surface is viewed at an angle to incident sunlight or incandescentlight. The patterns of fine grooves or clusters of groove segmentsembossed on the individual fibrous elements of the surface of thefibrous sheet continue to neighboring fibrous elements substantially inphase such that the distance between the last groove on one fibrouselement and the first groove on the neighboring fibrous element is amultiple (i.e., integer) of the groove width. Distinct rainbow orhologram images with good color, clarity and resolution are therebyproduced.

The invention also provides a process for preparing a fibrous sheet thatproduces rainbow or hologram images without detrimentally affectingdesirable attributes inherent in the sheet (e.g., breathability,flexibility, tactile aesthetics). In accordance with the process of theinvention, (a) a sheet of fibrous elements is softened by either heat ora chemical agent, depending on the nature of the fibrous elements; (b)the surface of the softened fibrous sheet is brought into contact withthe surface of a hard embosser having a pattern of fine grooves in thesurface; (c) sufficient pressure is applied to embosser to cause thegroove pattern to be embossed into the surface of fibrous elements onthe surface of the sheet and (d) then the sheet is collected. Typically,the pressure is applied by the plates of a platen press or a pair ofcooperating cylindrical rolls. The pressure is applied to the sheet fora time sufficient to emboss the embosser groove pattern to the surfaceof the outermost fibrous elements of the fibrous sheet. When embossingfibrous sheets of thermoplastic polymer, use of higher temperaturespermits the use of lower embossing pressures and use of higher embossingpressures permits the use of lower embossing temperatures. Note that thesteps of softening, heating and applying embosser pressure can beperformed simultaneously or in any other order found advantageous for aparticular fabric. To assure accurate transfer of the micron groovepattern of the embosser to the fibrous sheet, the embossing pressure isapplied uniformly over the affected area of the sheet and stretching ofthe sheet is avoided when the sheet is removed from the embossingequipment.

The accurate transfer of the fine groove pattern to the fibrous sheetcan be accomplished conveniently with a platen press, as illustrated inFIG. 1. In accordance with this method, a fibrous sheet 10 and anembossing stamper 12 are placed between two release sheets 13, 13' of adimensionally and thermally stable material (e.g., ARMALON®, aTEFLON®-perfluoroethylene coated glass fabric) to form a first assembly.The first assembly is then placed between two heat resistant soft rubbersheets 14, 14' (e.g., of VITON® or silicone rubber) to form a secondassembly. The second assembly is then placed between two flat plates 15,15' of sheet metal to form a composite sandwich. The composite sandwichis then placed between platens 16, 16' in a flat platen press that waspreheated to a desired temperature. Pressure is then applied for apredetermined time, after which the sandwich is removed from the pressand the embossed sheet structure is separated from the stamper.

For sheets comprising fibrous elements of a thermoplastic polymer, suchas a polyolefin, a polyamide or a polyester, the suitable temperaturefor the embossing is in a range between the softening temperature andthe melting temperature of the fibrous material under the pressureapplied during embossing. For a sheet comprising two types of fibrouselements, each formed from a different thermoplastic polymer, a suitabletemperature for embossing the sheet usually is between the meltingpoints of the two polymers. At such temperatures, the embossed patternof fine grooves can provide the fabric surface with a clear rainbow orhologram image. The intensity of the resultant image pattern isincreased by more intense embossing conditions, especially by increasedpressure and temperature. However, at increasingly higher embossingtemperatures there is a gradual increase in the tendency of the fibersto deform, interlock and even bond together at crossover points, with anattendant reduction in fiber mobility, breathability, flexibility andtactile aesthetics. If excessive temperatures and pressure are employed,the fibrous elements can melt and the sheet can become an impermeablefilm. Also, it is preferred that prior to embossing, the fibrous sheetshould be scoured or washed free of materials such as spinning finish,size and gums used during fiber or fabric processing in order to avoidfouling of the embossing pattern of the stamper and minimize theevolution of smoke at the embossing temperatures.

The optimum embossing conditions for a particular fabric or sheet can bedetermined without undue experimentation, through a simple series ofshort tests at different temperatures, pressures and embossing times, inthe particular equipment that is to be used. The optimum embossingconditions are those that provide the best looking rainbow orholographic images without sacrificing the desirable properties offabric breathability, flexibility and tactile aesthetics. Such a seriesof tests run with a platen press on the woven nylon fabric of Example 1below showed optimum embossing conditions to be a temperature of about200 to 225° C., for 3 to 5 minutes, at a calculated pressure of 1,275 to2,585 KiloPascals (185 to 375 psi) based on the area enclosed by therigid steel plates 15 and 15' or a pressure of 17,595 to 35,673 Kpa(2,498 to 5,175 psi) based on the area enclosed by stamper 12.Substantially the same optimum conditions were found for the other nylonfabrics and the polyester fabrics of the Examples below. A similarseries of preliminary tests on the polyethylene spunbonded sheet ofExample 8 below showed the optimum embossing conditions to be about 3minutes at a temperature in the range of 90 to 100° C. and a pressure inthe range of 208 to 448 KPa (30 to 65 psi) based on the area enclosed byplates 15 and 15' or a pressure of 2,870 to 6,182 KPa (414 to 897 psi)based on the area of stamper 12. Example 12 showed that for a warp-knitpolypropylene fabric in a continuous embossing process operating at alinear throughput of about 3 cm/minute, satisfactory results could beobtained at temperatures in the range of 135 to 150° C., with pressuresof at least 1,310 KPa (190 psi). Typically, the intensity of thediffraction pattern, produced under optimum conditions is not as brightas a similar pattern produced on film. However, the optimum pattern isclearly visible and has an attractive, relatively subdued brightness,which makes it more desirable for apparel end uses than the flashypatterns typically produced on films.

For fibrous sheets made from fibrous elements that are notthermoplastic, such as cotton, rayon, cellulose or the like, prior toembossing, the sheet can be softened by treatment with a chemicalsoftening agent, such as a swelling agent, plasticizer or partialsolvent for the fibrous elements. After softening of the fibrouselements at the surface of the sheet, the fibrous sheet can be subjectedto embossing under pressure in a manner substantially similar to thatdescribed for embossing sheets formed with thermoplastic elements.However, embossing or drying temperatures greater than the boilingtemperature of the softening agent are avoided to prevent bubbleformation.

In addition to the batch or stepwise process and equipment describedabove with regard to FIG. 1, the process of the invention also can beperformed in a continuous manner with roll embossing equipment, asillustrated in FIGS. 2 and 3, with or without sheaths on the rubberback-up rolls. The same type of equipment, modified for higher embossingtemperatures and pressures, is also suitable for embossing sheets orfabrics made from fibrous elements of higher melting temperaturethermoplastic polymers, such as polyesters and polyamides. The equipmentof FIG. 2 is more suitable for high production rates on a commercialscale and is particularly suited for embossing sheets or fabrics offibrous elements made from thermoplastic polymers having relatively lowmelting temperatures (e.g., polyolefins). As illustrated in FIG. 2, asheet or fabric 21 of thermoplastic fibrous elements, is advanced from asupply roll 22, under idler roll 23, through a nip formed byrubber-sheathed back-up roll 24 and heated metallic embossing roll 25,and then to embossed sheet wind-up roll 26. This equipment can also beused, with or without a rubber sheath on the back-up roll, with fabricsmade from higher melting fibers, such as polyamides and polyesters,provided that the embossing roll temperature is raised sufficiently andthe roll speed is sufficiently reduced to improve heat transfer to thesheet surface and attain the desired softening temperature.

FIG. 3 depicts continuous process equipment more suited than theequipment of FIG. 2 for embossing diffraction patterns and hologramimages on sheets or fabrics made from fibrous elements of polymers withrelatively high melting temperatures (e.g., polyamides, polyesters). Theequipment of FIG. 3 also permits higher speed embossing. As depicted inFIG. 3, fibrous sheet 31 is advanced from supply roll 32 over a set ofheated idler rolls 33, 33' and 33" to heated metallic embossing roll 37and then to embossed product wind-up roll 38. The heated rolls aredesigned to provide larger wrap angles and contact areas (as compared tothe rolls of the equipment of FIG. 2) with a minimum of non-heated spacein between the rolls. Rubber-sheathed roll 35 transmits pressure againstembossing roll 37 through endless belt 36 made of a release material(e.g., ARMALON®) which runs around roll 35 and idler rolls 34 and 34'.To further improve the heat transfer and raise the fabric embossingtemperature more rapidly, the entire system of heated idler rolls,heated embossing roll, rubber roll and release belt is enclosed ininsulated chamber 39. Optionally, the sheet surface to be embossed, canbe further heated by radiant heaters (not shown) located between idlerroll 33" and embossing roll 37.

The processes illustrated in FIGS. 1, 2 and 3 for embossing rainbow orhologram images on fibrous sheets also can be performed in combinationwith conventional embossing of the sheets with large macroscopic sizegrooves or other relatively large relief patterns, in simultaneous orseparate embossing steps. The simultaneous embossing of a hologram and amacroscopic relief pattern can be accomplished with equipment of thetype depicted in FIG. 1. For example, a metal embossing plate having amacroscopic relief pattern (e.g., a screen mesh or a plate having awaffle pattern) can be placed under fibrous sheet 10 and over, or inplace of, release sheet 13', with the relief surface facing the bottomof sheet 10, with the other equipment components of FIG. 1 remaining thesame. Such simultaneous embossing of the fibrous sheet with macroscopicand hologram patterns subjects localized regions of the fibrous sheetalong the macroscopic relief pattern to higher pressures than thesurrounding areas. As a result, the regions subjected to higherpressures become somewhat thinner, develop deeper holographic groovesand exhibit stronger diffraction colors. The fibrous elements in thehigh pressure regions become more strongly consolidated and theirembossed configurations become more durable and resistant to handling,washing and ironing. The thusly embossed fibrous sheet also has aspecial surface texture and reduced sheen. These added characteristicsenhance the tactile and visual aesthetics and durability of fibroussheets embossed with rainbow or hologram images.

As noted above, breathability, flexibility and tactile aestheticproperties of the fibrous sheet are substantially unaffected when apattern of fine grooves is embossed in the surface of the fibrous sheetin accordance with the process of the invention. Some flattening of theembossed surface of the fibrous elements and some reduction in sheetthickness usually accompany the embossing, but negligible bonding occursat fibrous element cross-over points, beyond that which already existsin the sheet or that which is intended to be developed during thermalembossing of fibrous sheets containing secondary filaments or particlesof lower melting temperatures which are included to produce some patternbonding or point bonding in the sheet structure.

In applying a fine-groove embossing pattern to a fabric according to theinvention, the relative direction of the grooves and the filaments inthe fabric has little effect on the resultant images. Substantially thesame effect is obtained if the fine grooves are parallel, perpendicular,or at an angle to the filament axis. Also, the visibility of the rainbowand hologram images are substantially the same whether the fabric is wetor dry. Further, substantially the same quality of rainbow and hologramimages can be obtained with fabrics in which the filaments are twisted,interlaced, cut, continuous, oriented, ordered or random or of round orother cross sections. However, for maintenance of the integrity of theembossed patterns, sheets or fabrics having embossed surfaces of highdimensional stability, such as woven, point bonded or pattern bondedfabrics, are highly desirable. Also, the fine groove patterns can beembossed on fibrous sheets of different colors, which containconventional dyes, pigments or printed surface decoration, therebyadding dynamic colors and holographic images to the visual aesthetics ofsuch sheets.

The rainbow and holographic images produced by the embossed pattern offine grooves are best seen under the bright sunlight or brightincandescent lights. Accordingly, embossed sheets and fabrics of theinvention are particularly suited for outdoor end uses, on stage, or inany other well lighted environment. Fibrous sheets and fabrics of theinvention can be used in upholstery, decorative fabrics or papers,draperies, window shades, cvarpets, luggage, clothing, sportswear, beachwear, swim wear, ski wear, stage costumes, boat sails, parachutes, andthe like.

EXAMPLES

The following examples illustrate the invention with the embossing offine groove patterns on the surfaces of various woven, knit and nonwovenfabrics to produce rainbow or holographic images. Each of fabrics of theexamples are made with thermoplastic fibers of nylon, polyester,polypropylene or polyethylene. Except for Example 12, each exampleemployed an assembly of the type depicted in FIG. 1 to emboss thefabric.

Example 1

In this example, a rainbow image is produced on the surface of a wovennylon fabric by embossing the fabric with a diffraction grating in aheated platen press. A 109-g/m² oxford fabric, woven with 25 by 20 endsper cm from 220-decitex, 34-filament yarn, the filaments being ofcircular cross-section and formed of bright nylon 66, was scoured, driedand ironed to remove any finish and size. A 19-cm-by-24-cm swatch of thefabric was then used as the fibrous sheet 10 of FIG. 1. A hard embosser12 (i.e., "stamper") in the form of a 10-cm-by-5-cm nickel sheet havinga diffraction grating pattern on its embossing surface was employed. Thediffraction grating consisted of parallel fine grooves spaced 1.3micrometers apart. The stamper was placed, with the grooves in parallelorientation to the fabric weave, in the middle and on top of the fabricswatch. Release sheets 13 and 13' of ARMALON® TEFLON®-coated glassfabric, 0.16-cm thick rubber sheets 14 and 14' and 0.16-cm-thick,30-cm-long, 23-cm wide stainless steel plates 15 and 15', were arrangedabove and below the fibrous sheet and stamper as shown in FIG. 1. Theresulting assembly was placed in a 30-cm-by-30-cm Pasadena hydraulicplaten press. The platens 16 and 16' were preheated to 215° C.; thepress was closed; and for 3 minutes, a load of 9,600 Kg was applied(corresponding to a pressure of 1,350 KPa, or 196 psi, based on the areaenclosed by rigid stainless steel plates 15 and 15', or to a pressure of18,630 Kpa, or 2,705 psi, based on the area enclosed by stamper 12 ).The pressure was then released and the entire assembly removed from thepress, placed on a table and allowed to cool under ambient conditions.After 3 minutes of cooling, the sandwich was separated into itscomponent layers and the fabric was allowed to cool further to roomtemperature. Because a burning rubber smell was noted during theembossing, indicating some degradation of the rubber sheets 14 and 14',all subsequent embossing examples which employed assemblies of the typeshown in FIG. 1 were conducted with temperature-resistant VITON® orsilicone rubber sheets.

Examination of the embossed nylon fabric revealed that the surface areaof the embossed region had become more shiny than the not-embossed areaof the swatch, but the embossed area apparently did not suffer anydamage to the weave pattern or lose any pliability and gas permeability.When the embossed surface was viewed at an angle relative to incidentlight from the sun or from an incandescent lamp, shimmering rainbowimages became visible in different areas of the fabric depending on theorientation of the specific fabric area relative to the incident light.These rainbow images extended to the length of the embossed area andcould be rolled over the fabric by holding one end of the fabric withone hand and raising or lowering the other end. The embossed swatch ofwoven nylon fabric was then washed and tumble dried in householdlaundering equipment and thereafter ironed with a hand iron on anironing board. The resulting fabric continued to show the same rainbowimages with the same intensity as before washing and ironing. Thediffraction grating pattern embossed on the fabric was very stable.Scanning electron photomicrographs of a duplicate fabric sample preparedunder identical conditions, showed the groove patterns on the filamentsurfaces in parallel orientation within and across the filaments in boththe fill and the warp directions.

Example 2

The demonstration of Example 1 was duplicated except that Viton® rubberinstead of the ordinary rubber sheets were employed and a slightly lowerpress embossing temperature was used (212 vs. 215° C.). Except for theelimination of the rubber-burning odor, the embossing results were thesame as those obtained in Example 1. The thusly embossed fabric was thensubjected to a laboratory-scale beck-dyeing process along with acomparison fabric swatch that was not subjected to the embossingprocess. At the end of the dyeing procedure with acid blue 120 dye, thedried and ironed fabric swatches were compared visually. The embossedswatch was found to have retained its ability to produce rainbow imagesbut had a somewhat lighter dyed blue shade, both within and outside theembossed area, than the comparison swatch. Apparently, this effectresulted from an increased degree of crystallinity in the fiber polymerand reduced dye uptake, which were caused by the heat treatment of thefabric during the embossing.

Example 3

In this example, a plain weave white fabric consisting of 34 by 39 endsper cm of fine decitex nylon 66 containing titanium dioxide delustrantand weighing 63 g/m² was embossed with the same stamper and under thesame conditions as used in the preceding examples, but at a temperatureof 214° C. The resulting embossed region of the fabric also producedfaint rainbow images upon exposure to the light from an incandescentlamp and strong rainbow images under sunlight.

Example 4

In this example, a Carver press with electrically heated, 23-cm-by-23-cmplatens was employed with the diffraction grating stamper of thepreceding examples to emboss a dyed-gray, heavy, nylon-66 twill fabricof 17-by-26 ends/cm weighing 233 g/m². The embossing was conducted at atemperature of 225° C. with a load of 9,800 Kg for 3 minutes(corresponding to a pressure of 1,835 KPa or 266 psi, based on the areaenclosed by the rigid platens, or to a pressure of 19,414 KPa or 2,814psi, based on the area enclosed by the stamper), followed by a coolingperiod of 3 minutes. Strong rainbow images were easily visible when theresultant embossed fabric was viewed under an electric lamp or sunlight.

Example 5

In this example, a turquoise-colored, ANTRON® nylon/LYCRA® spandex,warp-knit swimwear fabric was embossed under the same conditions as wereemployed in Example 4. The fabric was knit with 19 wales/cm and 19courses/cm and weighed 170 g/m². The fabric comprised 85% by weight of44-dtex, 13-trilobal-filament, semi-dull nylon-66 yarn and 15% by weightof 44-dtex, coalesced-4-filament LYCRA® spandex yarn. The embossedfabric developed bright rainbow images, as in Example 4. Following asevere manual stretching and relaxation of the fabric in the diagonaldirections, the intensity of the rainbow image was diminished but noteliminated.

Example 6

A woven, lightweight, white, polyester lining fabric having 41-by-28ends/cm and weighing 50.5 g/m² was embossed with the diffraction gratingpattern of the preceding Examples in the Carver press at a temperatureof 200° C. under a load of 16,350 Kg (corresponding to a pressure of3,060 KPa or 444 psi based on the area enclosed by platens 16, 16' or toa pressure of 32,375 Kpa or 4,706 psi based on the area enclosed bystamper 12). Upon release of the load, the fabric was immediatelyremoved from the embossing assembly and allowed to cool. The resultantembossed fabric exhibited rainbow images similar to those exhibited bythe nylon fabrics of Examples 1-4.

Example 7

A white satin Monice polyester fabric weighing 130 g/m² and having oneface with long floats and 19-by-25 ends/cm and a back face (the satinside) with 33-by-28 ends/cm, was embossed with the diffraction gratingstamper of the preceding examples under the same conditions as employedin Example 6. The fine grooves of the stamper were parallel to the longfloats. The resultant embossed portions of the fabric exhibited rainbowimages when subjected to the light from an incandescent lamp.

Example 8

A swatch of 45.4 g/m² TYVEK® spunbonded olefin, a nonwoven sheet formedof randomly deposited plexifilamentary strands of polyethylene filmfibrils was cut from a disposable uniform. The nonwoven polyethylenesheet sample was embossed in an assembly of the type shown in FIG. 1between the platens of the Carver Press (described in Example 4) at atemperature of 90° C. and for 3 minutes under a load of 2,273 Kg(corresponding to a pressure of about 427 KPa or 62 psi based on thearea enclosed by platens 16, 16' or to a pressure of 4,517 Kpa or 657psi based on the area enclosed by stamper 12). Rainbow images werevisible in the embossed area of the sheet when the sheet was viewed atan angle to incident incandescent light or sunlight. Scanning electronphotomicrographs of the embossed surface area showed faint fine groovesof the diffraction pattern on the randomly distributed plexifilamentarystrands of the TYVEK® fabric.

Example 9

In this example, the diffraction grating stamper of the precedingExamples was replaced with a 16.5-cm-by-16.5-cm hologram stamper sheetcontaining nine 4.2-cm-by-4.2-cm hologram pictures of different sportsactivities. The same white satin Monice polyester fabric as was used inExample 7 was also used in this example. An assembly of the typedepicted in FIG. 1 containing the fabric and the hologram stamper waspressed in the Carver press (described in Example 4) at a temperature of210° C. under a load of 13,600 Kg for 3 minutes (corresponding to apressure of 2,516 KPa or 365 psi based on the area enclosed by platens16, 16' or to a pressure of 4,517 Kpa or 657 psi based on the are ofstamper 12). The assembly was not allowed to cool before the fabric wasseparated from the assembly. The embossed area exhibited the coloredhologram images of the original hologram stamper when the embossed areasof the fabric were viewed at an angle to incident sunlight or light froman incandescent lamp. Just as in the stamper itself, the images werecomplete, continuous and uniform.

Example 10

This example repeats Example 9, except that (a) the fabric beingembossed was a red satin twill made from 220-decitex nylon yarn, (b) thepressing temperature was 225° C. and (c) the assembly was allowed tocool for three minutes before the embossed fabric was separated from theassembly. As in Example 9. the embossed fabric reproduced the hologrampictures of the of original embossing stamper. The hologram images fromthe embossed fabric surface were complete and continuous when viewed atan angle to incident light from an incandescent lamp or sunlight.

Example 11

In this example, a parachute fabric weighing about 30 g/m² was embossedin an assembly similar to that depicted in FIG. 1 with the diffractiongrating stamper in the Pasedena press of Example 1 at a temperature of215° C. under a platen load of 9,545 Kg for 3 minutes (corresponding toa pressure of 1,350 KPa or 196 psi based on the area enclosed by platens16, 16' of to a pressure of 18,630 Kpa or 2,705 psi based on the areenclosed by stamper 12). The fabric was made from, high tenacity,33-dtex, 10-filament, bright, nylon-66 yarns in a "rip-stop" squarewoven configuration with repeating cycles of 14 single ends/cm followedby two double ends and a total of 2.6 cycles/cm in both directions. Thefabric was dimensionally stable (i.e., it was not stretchable). Eventhough the fabric was of very light weight and had a relatively openconstruction, the embossed fabric exhibited a clear, continuous rainbowimage when the surface was viewed at an angle to incident sunlight orincandescent light.

Example 12

This example illustrates the embossing of a warp-knit polypropylenefabric. The equipment employed was of the type depicted in FIG. 2. Asnoted below, with the particular equipment used, the embossing pressurein the nip of the rolls was insufficient to permit continuous embossingof the fabric at commercially desired speeds. However, the results didindicate how such a continuous run could be accomplished. The particularfabric employed in this example was a 127-cm-wide, black, polypropylene,double-knit fabric with a "Ponta di Roma" construction. The fabric,which had 12.6 courses per cm and 6.3 wales/cm, weighed 205 g/m².Commercial, continuous, 152-cm-wide roll embossing equipment of the typeusually used for embossing holograms on plastic films, was employed.Initially an embossing test was run with a 180 degree fabric wrap angleon metallic embossing roll 25, and with the embossing roll operating ata surface temperature (measured with an infrared thermometer) of 135°C., which was very close to the 138° C. softening point of thepolypropylene yarns. Metal embossing roll 25 and rubber roll 24 (havinga Shore A durometer hardness of 70) formed the nip through which fabric21 passed at a linear speed of 60 cm/min, the minimum speed achievablewith the equipment. The temperature of the fabric leaving the roll was120° C. The embossing pressure on the nip formed by rolls 24 and 25 wasset at the highest that could be achieved with the equipment. Underthese conditions, with fibrous sheet speed at 60 cm/min, satisfactoryembossing of the fabric was not achieved. However, under the sameconditions of temperature and load, but with the fabric being allowed toremain in the nip between rolls 24 and 25 for 30 seconds, satisfactoryembossing of the hologram pattern was obtained on the area contacted inthe nip. The width of the embossed contact area measured about 1.52 cmnear the edge of the fabric and about 1.27 cm near the center of thefabric, indicating that the pressure was non-uniformly distributedacross the entire width of the fabric. When these embossed areas wereviewed at an angle to incandescent light or sun light, a clear colorfulhologram pattern was apparent. From the dimensions of these embossedareas and the load applied thereto, the pressure in the nip wascalculated to be about 1,288 KPa (187 psi) in the area at the fabricedge and about 1213 KPa (176 psi) in the area near the center of thefabric. When the embossed area of the fabric was hand-stretched in themachine direction, the hologram pattern substantially disappeared, butreappeared when the fabric was allowed to relax, indicating that theembossed fine grooves returned to their original position, in registerwith the grooves of adjacent filaments. The above-stated results showthat a successful continuous process for embossing a hologram pattern onthe polypropylene fabric of this example could be achieved at a speed ofabout 3 cm/minute with the temperatures and pressures employed in thisexample. Also, preheating of the fabric, higher temperatures (below thepolymer melting temperature) and higher, more uniform nip pressureswould be needed to perform continuous hologram embossing at higherspeed.

Example 13

This example illustrates embossing rainbow or hologram diffractionpatterns on a 190-g/m² polyester satin fabric, similar in constructionto the fabric of Example 7, with an electrically induction heatedstamper.

Equipment similar to that illustrated in FIG. 1 was modified for usewith electrical induction heating instead of oil or electricalresistance heating. Release sheet 13, rubber sheet 14 and flat metalplates 15 and 15' were not included in the equipment. Hard metalembosser 12 (i.e., the "stamper") was attached to platen 16 with a hardelectrical insulating layer sandwiched between the stamper and theplaten. The embossing surface of stamper 12 was arranged to face thesurface of the fibrous sheet 10 that was to be embossed. The embossingstamper was a metal plate having a 7.6 cm×7.0 cm area with a "QuarterInch Square" holographic pattern. Fabric samples were embossed by (a)assembling a fabric sample (i.e., fibrous sheet 10), release sheet 13'and the rubber sheet 14'; (b) placing the thusly formed assembly betweenthe lower platen 16' and hard embosser surface which is attached toupper platen 16; (c) closing the platens on the assembly; (d) applyingpressure to platen 16; (d) sending an electrical induction currentthrough the metal embosser 12 for a predetermined period of time,referred to as "power time"; (e) maintaining the pressure for anadditional period of time, referred to as "settling time"; (f) releasingthe pressure and lifting upper platen 16; and (g) removing the assemblyand separating the embossed fibrous sheet therefrom. Note that, in thisequipment, the embossing temperature could not be measured directly.Instead, the induction current and the power time were used incombination as an indirect measure of fabric temperature. The equipmentwas operated manually.

A small number of trials were performed to determine the optimumembossing conditions needed to produce fabric samples having,subjectively judged, "very good" hologram images and "very good" wrinkleresistance. The optimum conditions were a pressure of 8,360 KPa, and aninduction current of 280 ampere applied for 10 to 13 seconds power timeand followed by a 7-second a settling time. Under more severe embossingconditions, a power time of 15.5 seconds and settling times of 16 to 35seconds, provided fabric samples with "excellent" holographic images andwrinkle resistances, but some filament-to-filament melt cohesion (i.e.,some fusion) occurred in an area of about 5 cm² in the center of theembossed area. The fused area was translucent when viewed by transmittedlight while the rest of the area surrounding it was opaque. Under milderembossing conditions (i.e., decreased power time), the color intensityof the hologram images decreased from "very good" to "good" when powertime was 8.5 seconds and to "faint" when power time was 6.5 seconds. Thecorresponding resistance to wrinkling also diminished to "medium" and"poor", respectively. These tests also showed that fabric thicknessdecreased with increasing severity of embossing conditions. Thethickness decrease trend was accompanied by corresponding increases inthe brightness of the hologram images and increases in the wrinkleresistance of the fabric. For this polyester satin fabric, a decrease inthickness of 30-35% was accompanied by good wrinkle resistance. Poorwrinkle resistance was obtained when the thickness decrease was only20-30%. Microscopic examination of the surface of the optimally embossedfabric showed that the yarns, at the weave crossover points, wereflattened, and that the surface filaments were tightly held together,and well anchored to filaments below the surface, but without any meltfusion. Increased wrinkle resistance was found to accompany the greaterflattening.

Example 14

This example illustrates the use of semi-continuous, "step-and-repeat"holographic embossing equipment for embossing relatively large pieces offibrous sheets. The same polyester satin woven fabric as was used in theExample 13 was used as the fibrous sheet in this example. The equipmentwas fitted with an indexed, moving fabric-feeding table to increaseproduction speed and to more precisely place embossing patterns inpredetermined locations on the surface of a fibrous sheet or fabricsample. The embossing equipment was moved to specific areas of fabricsurface under the embossing stamper and was automatically controlled topre-specified time intervals and embossing conditions. The specificassembly of fabric 10 and equipment components were the same asdescribed in Example 13, except that in this example no release sheets13, 13' were used at all. Fabric 10 was placed on top of the 0.16-cmthick silicone rubber sheet 14' which in turn was placed on a flat rigidplate 15' made of plastic instead of metal This assembly was thenfastened to a metal tray and moving arm of the indexing system. Theindexing system was programmed to emboss 5.7-cm×7.6-cm areas of thefabric (with a stamper of equal dimensions) spaced 1.5-cm apart in thelongitudinal direction and 0.64-cm apart in the transverse direction ofthe feeder.

Six panels of "Quarter Inch Square" holographic patterns were embossedon a 38-cm×38-cm area of fabric with the equipment described in thepreceding paragraph with an 5-ton embossing load (equivalent to apressure of 10,134 KPa or 1,481 psi), a 300-ampere induction current, a22-second power time and a 25-second settling time. The hologramquality, in terms of clarity and brightness on exposure to direct light,was "excellent" in all six panels. The holographic patterns were uniformwithin each panel and from panel to panel, with no signs of filamentfusion anywhere on fabric surface. As a result of the embossing, thethickness of the fabric decreased by 30% from 0.20 mm before embossingto 0.14 mm after embossing.

This Example 14, along with Examples 12 and 13, indicate that thecomplicated, multi-layer assembly employed in the batch process of FIG.1 and the earlier illustrative examples herein, can be significantlysimplified. In a continuous or semi-continuous processes, the fabric canbe placed directly between the stamper embossing surface on one side andthe rubber surface on the other side, with a release sheet between thefabric and the rubber sheet as in Example 13 and FIG. 3, or withoutrelease sheet as in Examples 12 and 14 and FIG. 2.

I claim:
 1. A process for making a fibrous sheet that produces rainbowor hologram images, comprising the steps ofpreparing a sheet of fibrouselements; softening at least the fibrous elements on a surface of thesheet; placing the sheet on a supporting surface; bringing a hardembosser having a surface with a pattern of fine grooves thereon intodirect contact with the surface of the fibrous sheet having the softenedfibrous elements, the grooves being spaced apart uniformly by about 0.1to 10 microns and being at least 0.01 microns deep; imposing sufficientload on the embosser for a sufficient time to impress the pattern offine grooves into the surface of the softened fibrous elements on thesurface of the sheet with negligible bonding of fibrous elementcross-over points, the patterns of fine grooves on the individualfibrous elements of the sheet surface continuing to neighboring fibrouselements substantially in phase, with the distance between the lastgroove on one fibrous element and the first groove of the neighboringfibrous element being a multiple of groove width; separating the sheetfrom the embosser; and collecting the separated sheet.
 2. A processaccording to claim 1 wherein the fibrous elements comprise thermoplasticorganic polymer and the fibrous elements are softened by heating thesheet surface to a temperature above the softening temperature of thepolymer but below the melting temperature of the polymer.
 3. A processaccording to claim 2 wherein the fibrous sheet is a woven fabric or knitfabric comprised of polypropylene, polyester or nylon yarns.
 4. Aprocess according to claim 2 wherein the fibrous sheet is a nonwovenfabric.
 5. A process according to claim 4 wherein the nonwoven sheet isa spunbonded olefin sheet of plexifilamentary strands of polyethylenefilm fibrils.
 6. A process according to claim 1 wherein softening of thefibrous elements is performed before the fibrous sheet is placed incontact with the embosser.
 7. A process according to claim 1 whereinsoftening of the fibrous elements is performed while the fibrous sheetis in contact with the embosser.